Abstract: Stress relief annealing of TC18 and TC21 titanium alloys was carried out in a pit-type air furnace according to GJB3763A-2004 standard with the highest temperature and longest holding time, respectively. The effect of stress relief annealing on hydrogen absorption of TC18 and TC21 titanium alloys was studied. The results show that the hydrogen content of TC18 titanium alloy increases after stress relief annealing in air furnace compared with that before stress relief heat treatment, while that of TC21 titanium alloy decreases. The hydrogen content of TC18 and TC21 is 0.0029% and 0.0025% respectively, that is much lower than that of required by material specifications(<0.015%) after stress relief in the air furnace. After stress relief annealing, the hydrogen content of TC18 and TC21 titanium alloys change regularly with the change from surface to center (depth), and there is little difference between the hydrogen content of inner layer and that of surface layer. Considering the amount of hydrogen absorption, stress relief annealing can be conducted for the two titanium alloys by air furnace.

Key words: TC18 titanium alloy, TC21 titanium alloy, stress relief annealing, hydrogen absorption